# why does the figure doesnt show the two vectors?

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shamma aljaberi on 2 Nov 2023
Commented: dpb on 2 Nov 2023
Hi! i am working on a project using the while loop (similar to my question regarding for loop) the figure doesnt show the plot as desired. what is wrong regarding the code?
code below:
%Links length
L1=5; L2=1; L3=5; L4=7; AP=5;
% ternary link angle (degree)
delta=50;
th2= 0:1.2:360;
range_th2=300;
RP=zeros(1,range_th2);
RA=zeros(1,range_th2);
i=1;
while i<=301
% the loop variables
R1=L1;
R2=L2*(cos(th2(i))+sin(th2(i))*1i);
Z=R1-R2;
Zconj=conj(Z);
% Quadratic equation parameters
a=L4.*Zconj;
b=Z.*Zconj+L4.^2-L3.^2;
c=L4*Z;
T=roots([a b c]);
T_pos=T(2);
%T_pos=(-b+sqrt(b.^2-4.*c.*a))/(2.*a);
S=(L4*T_pos+Z)/L4;
% solution
th3(i)=rad2deg(angle(T_pos));
th4(i)=rad2deg(angle(S));
R3=L3*(cos(th3(i))+sin(th3(i))*1i);
R4=L4*(cos(th4(i))+sin(th4(i))*1i);
thAP=th3(i)-delta;
RAP=AP*(cos(thAP)+sin(thAP)*1i);
%position of A and P
RA(i)=R2;
RP(i)=R2+RAP;
i=i+1;
end
A_real=real(RA)
A_real = 1×301
1.0000 0.3624 -0.7374 -0.8968 0.0875 0.9602 0.6084 -0.5193 -0.9847 -0.1943 0.8439 0.8059 -0.2598 -0.9942 -0.4607 0.6603 0.9392 0.0204 -0.9245 -0.6903 0.4242 0.9977 0.2989 -0.7811 -0.8650 0.1543 0.9768 0.5536 -0.5756 -0.9707
A_imag=imag(RA)
A_imag = 1×301
0 0.9320 0.6755 -0.4425 -0.9962 -0.2794 0.7937 0.8546 -0.1743 -0.9809 -0.5366 0.5921 0.9657 0.1078 -0.8876 -0.7510 0.3433 0.9998 0.3813 -0.7235 -0.9056 0.0672 0.9543 0.6244 -0.5018 -0.9880 -0.2143 0.8328 0.8178 -0.2401
plot(A_real,A_imag)
hold on
P_real=real(RP)
P_real = 1×301
-3.8675 2.9171 -5.5663 -1.7785 -4.8323 1.6248 3.3844 1.8513 -1.5249 -2.4793 -0.2238 0.0130 4.5774 -2.5654 4.4553 5.4299 0.2248 2.6124 3.0542 -2.5154 -3.9619 -3.8939 -3.5367 -5.6547 -1.6590 -0.4626 5.1432 5.1124 -0.0507 1.6366
P_imag=imag(RP)
P_imag = 1×301
1.1434 -3.3660 1.9724 4.4791 -0.1042 4.6762 -3.3649 5.2569 -5.1451 3.4664 -5.4213 5.5288 -0.2998 4.8545 -1.8001 0.7494 -4.6054 -3.2759 -2.6469 -5.3785 1.4949 1.1027 -2.2532 -0.4928 4.4348 3.9738 2.5499 -1.2209 5.7901 -4.5064
plot(P_real,P_imag)
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### Answers (2)

Les Beckham on 2 Nov 2023
Edited: Les Beckham on 2 Nov 2023
It looks like it is working to me (see below). What are you expecting and how is that different from the results you are seeing?
%Links length
L1=5; L2=1; L3=5; L4=7; AP=5;
% ternary link angle (degree)
delta=50;
th2= 0:1.2:360;
range_th2=300;
RP=zeros(1,range_th2);
RA=zeros(1,range_th2);
i=1;
while i<=301
% the loop variables
R1=L1;
R2=L2*(cos(th2(i))+sin(th2(i))*1i);
Z=R1-R2;
Zconj=conj(Z);
% Quadratic equation parameters
a=L4.*Zconj;
b=Z.*Zconj+L4.^2-L3.^2;
c=L4*Z;
T=roots([a b c]);
T_pos=T(2);
%T_pos=(-b+sqrt(b.^2-4.*c.*a))/(2.*a);
S=(L4*T_pos+Z)/L4;
% solution
th3(i)=rad2deg(angle(T_pos));
th4(i)=rad2deg(angle(S));
R3=L3*(cos(th3(i))+sin(th3(i))*1i);
R4=L4*(cos(th4(i))+sin(th4(i))*1i);
thAP=th3(i)-delta;
RAP=AP*(cos(thAP)+sin(thAP)*1i);
%position of A and P
RA(i)=R2;
RP(i)=R2+RAP;
i=i+1;
end
A_real=real(RA);
A_imag=imag(RA);
plot(A_real,A_imag);
hold on
P_real=real(RP);
P_imag=imag(RP);
plot(P_real,P_imag)
axis equal
##### 2 CommentsShow NoneHide None
shamma aljaberi on 2 Nov 2023
Im expecting a circular shape for RA and more like an Ellipse shape for RP
Les Beckham on 2 Nov 2023
I edited my answer to add "axis equal" so the x and y scales are equal. They are both pretty circular in shape. Have you double checked the equations?

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dpb on 2 Nov 2023
Edited: dpb on 2 Nov 2023
%Links length
L1=5; L2=1; L3=5; L4=7; AP=5;
% ternary link angle (degree)
delta=50;
th2= 0:1.2:360;
range_th2=300;
RP=zeros(1,range_th2);
RA=zeros(1,range_th2);
i=1;
while i<=301
% the loop variables
R1=L1;
R2=L2*(cos(th2(i))+sin(th2(i))*1i);
Z=R1-R2;
Zconj=conj(Z);
% Quadratic equation parameters
a=L4.*Zconj;
b=Z.*Zconj+L4.^2-L3.^2;
c=L4*Z;
T=roots([a b c]);
T_pos=T(2);
%T_pos=(-b+sqrt(b.^2-4.*c.*a))/(2.*a);
S=(L4*T_pos+Z)/L4;
% solution
th3(i)=rad2deg(angle(T_pos));
th4(i)=rad2deg(angle(S));
R3=L3*(cos(th3(i))+sin(th3(i))*1i);
R4=L4*(cos(th4(i))+sin(th4(i))*1i);
thAP=th3(i)-delta;
RAP=AP*(cos(thAP)+sin(thAP)*1i);
%position of A and P
RA(i)=R2;
RP(i)=R2+RAP;
i=i+1;
end
A_real=real(RA);
A_imag=imag(RA);
plot(A_real,A_imag);
hold on
P_real=real(RP);
P_imag=imag(RP);
plot(P_real,P_imag);
axis equal
legend('A','P')
figure, subplot(2,1,1) % look versus order instead
plot(A_real), hold on, plot(A_imag)
xlim([1 100])
legend('A_R','A_I')
subplot(2,1,2) % look versus order instead
plot(P_real), hold on, plot(P_imag)
legend('P_R','P_I')
xlim([1 100])
What we observe is that the "A" traces are pretty clean sinusoids with just a phase difference; hence the real vs imaginary parts follow a decent trace as shown on the first.
On the other hand, the "P" traces are much more random appearing; movements aren't smooth from one observation to the next; hence the two plotted against each other reflect that...
What you were expecting is unknown to us...we don't know the problem statement.
##### 4 CommentsShow 2 older commentsHide 2 older comments
Voss on 2 Nov 2023
Fixing the degree/radian units issue, based on @dpb's observation, produces a more interesting plot. Maybe that's closer to what's intended, @shamma aljaberi?
%Links length
L1=5; L2=1; L3=5; L4=7; AP=5;
% ternary link angle (degree)
delta=50;
th2= 0:1.2:360;
range_th2=300;
RP=zeros(1,range_th2);
RA=zeros(1,range_th2);
i=1;
while i<=301
% the loop variables
R1=L1;
R2=L2*(cos(th2(i))+sin(th2(i))*1i);
Z=R1-R2;
Zconj=conj(Z);
% Quadratic equation parameters
a=L4.*Zconj;
b=Z.*Zconj+L4.^2-L3.^2;
c=L4*Z;
T=roots([a b c]);
T_pos=T(2);
%T_pos=(-b+sqrt(b.^2-4.*c.*a))/(2.*a);
S=(L4*T_pos+Z)/L4;
% solution
th3(i)=rad2deg(angle(T_pos));
th4(i)=rad2deg(angle(S));
R3=L3*(cosd(th3(i))+sind(th3(i))*1i);
R4=L4*(cosd(th4(i))+sind(th4(i))*1i);
thAP=th3(i)-delta;
RAP=AP*(cosd(thAP)+sind(thAP)*1i);
%position of A and P
RA(i)=R2;
RP(i)=R2+RAP;
i=i+1;
end
A_real=real(RA);
A_imag=imag(RA);
plot(A_real,A_imag)
hold on
P_real=real(RP);
P_imag=imag(RP);
plot(P_real,P_imag)
axis equal
legend('A','P')
figure, subplot(2,1,1) % look versus order instead
plot(A_real), hold on, plot(A_imag)
xlim([1 100])
legend('A_R','A_I')
subplot(2,1,2) % look versus order instead
plot(P_real), hold on, plot(P_imag)
legend('P_R','P_I')
xlim([1 100])
dpb on 2 Nov 2023
@Voss -- thanks, I got interrupted before I got a chance to look more to see if that was the only place -- maybe the alternative fix would be to simply remove the calls to rad2deg() unless the angles are being displayed in those units elsewhere.

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